This invention pertains to methods and apparatus for proving, verifying, or calibrating a flow meter of the type used to measure volume dispensed from a storage receptacle. In particular, the method and apparatus are used for proving, verifying, or calibrating flow meters used in the dispensing of cryogenic fluids (cryogens) from storage tanks, mobile trailers, and the like.
Calibration of cryogenic flow meters is usually accomplished by comparing the meter under test against a given volume of fluid dispensed into a tank and weighed. Such testing is normally accomplished in a laboratory environment using a flow loop in which the meter to be tested is installed. The meter is physically removed from the trailer or dispensing apparatus and sent to the laboratory. The flow loop consists of a cryogenic storage vessel, a pump, a weighing system, and a receptacle so that the precise weight can be obtained and the amount of fluid dispensed calculated for calibrating the meter. The flow loop testing has some disadvantages in that the piping and other equipment may not duplicate the in-service environment, e.g. a large number of flow meters are affected by changes in the geometry of the associated piping. The use of truck platform scales is undesirable because of the fact that such scales can be subject to errors caused by the wind, accumulated moisture, and other environmental factors at the test site. Furthermore, a flow loop would normally be required in each state or used among the several states. Normally, one state will generally not accept the flow loop testing of another state.